2024-04-25-世界卫生组织-Joint_FAO_WHO_WOAH_preliminary_assessment_of_recent_influenza_A_H5N1_viruses_8页_310kb

Summary of Joint FAO/WHO/WOAH Preliminary Assessment of Recent Influenza A(H5N1) Viruses

Since 2020, highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b viruses have emerged and spread globally through migratory birds, causing unprecedented mortality in wild birds, outbreaks in poultry, and detections in various animal species. As of late 2021, including North America and subsequently South America, these viruses have been found in non-avian terrestrial and marine mammals, notably dairy cattle in the United States, leading to lateral transmission concerns.

Human cases of A(H5N1) infection surged from 2021, with 28 reports by 2024, primarily involving direct or indirect exposure to infected birds, mammals, or contaminated environments. Clade 2.3.4.4b was involved in 13 cases, often resulting in mild symptoms like fatigue or conjunctivitis, though a few severe cases occurred, including one death and fatalities in Asia. Genetic analysis shows limited adaptation markers in human cases but no significant changes increasing airborne transmissibility.

Risk assessments by WHO, FAO, and WOAH indicate a low overall public health risk for widespread human-to-human transmission, as the viruses remain well-adapted to birds and have not demonstrated sustained human-to-human spread. However, the risk for humans handling infected animals, especially cattle or dairy products, is moderate due to high viral loads in milk and potential for zoonotic spillover. Cattle-to-human transmission is possible, with dairy cattle in the US showing high milk contamination, but pasteurization may mitigate risks.

Key recommendations include enhancing surveillance in animals and humans, reporting outbreaks to international organizations, enforcing biosecurity measures, monitoring zoonotic infections, and advocating for pasteurized milk consumption to reduce exposure risks. Ongoing research and rapid data sharing are urged to update risk assessments as the virus evolves.